Floppy magnetic recording discs are flexible discs of polyester resin or the like having a magnetic layer on each side thereof on which information is recorded by a magnetic head. Floppy discs which have a diameter of 31/2 inches (8.9 cm) or less are known as micro-floppy discs. Generally, the micro-floppy disc is accommodated in a hard casing to form a cartridge. The micro-floppy disc comprises a circular magnetic recording medium which is thin, has a small diameter, and has a hub fixed to the center of the recording medium.
The cartridge generally includes a fabric liner on both inner surfaces of the casing. The liner is kept in contact with the recording surface of the disc to remove debris on the recording surface while the disc is rotated. The liner has a width at least equal to the width of the recording region of the disc, and is kept pressed against the entire width of the recording surface by a lifter which is secured to the inner surface of the casing.
As explained in U.S. Pat. No. 4,739,433 (Oishi), it is desirable to have the lifter exert more pressure on the inner data tracks of the disc than on the outer data tracks. This is so because the recording density of the disc is greater at its inner tracks, which results from the fact that the same amount of information is recorded during one rotation of the disc regardless of which data track is being recorded on. Thus, debris which might not cause a problem on an outer data track can cause loss of data ("drop-outs") in the reading of data on the inner tracks. It is, therefore, desirable to clean the inner tracks more thoroughly than the outer tracks.